Method of treating metal alloys



V. T. MALCOLM METHOD OF TREATING METAL ALLOYS Filed April 24. 1933 JZ Z.JJE

ATTORNEY,

Patented Oct. 3, 1933 UNITED STATES PATENT OFFICE METHOD OF TREATINGLIETAL ALLOYS tion of Massachusetts Application April 24, 1933. SerialNo. 667,677

6 Claim.

This invention relates to improvements in apparatus for and methods oftreating metal alloys to provide hardened surfaces therefor.

The principal objects of this invention are directed to improvements inmethods and apparatus for supplying substantially active nitrogen to afused salt bath for treating alloy metals such as steels and the like toprovide hardened surfaces therefor. According to special features of theinvention it is possible to treat relatively low-price steels so thatthey will have the desirable characteristics of more expensive orspecial steels, and the desired surface-hardening effects may be broughtabout at extremely low cost.

I have discovered that it is possible to obtain very favorable resultswhen relatively inexpensive steels are used by supplying a suitablehardening bath with active nitro en. That is to say, when a suflicientamolfit o f active nitrogen is supplied the bath, I have found thatrelatively inexpensive steel may be treated to provide hardened surfacesin a comparatively short'space of time which are equal, if not superior,to what may be expected of more expensive steels. Therefore, myinvention is directed to the provision of a novel method and apparatusadapted to supply the necessary and desired amount of active nitrogen tothe hardening bath for the treatment or surface-hardening effects.

Various novel features and advantages of the invention will be morefully hereinafter referred to in connection with the accompanyingdescription thereof. The novel method of the invention may be carriedout by means of various forms of apparatus but one form of an apparatuswhich has been found to be satisfactory for the purpose of the inventionis hereinafter described and shown in the accompanying drawing, wherein:

Fig. 1 is a diagrammatic elevational view of an apparatus adapted forcarrying out the novel method of the invention.

Fig. 2 is a sectional elevational view through the dissociator unit ofthe invention.

Fig. 3 is an elevational sectional view through the ionizer unit of theinvention with an electrical diagram associated therewith, and

Fig. 4 is a plan view of the central electrode of the ionizer unit.

Referring now to the drawing more in detail the novel apparatus andmethod of the invention will be fully described.

As previously stated, one of the objects of the invention is to providea supply of active nitrogen to a hardening bath in which the alloy isbeing treated. This is desirable for the best hardening effects andmakes it possible to operate on relatively inexpensive materials andobtain the desired hardness in a relatively short time and in that wayprovide material having hardened surfaces at extremely low cost.

To supply nitrogen for the bath, I employ a nitrogen-containing gas,such as ammonia. Before it is delivered to the bath, it is subjected tocertain reactions in accordance with the invention as will presentlyappear so that substantially free active nitrogen enters the bath forits function in connection with the hardening operation.

In some instances, it may be desired to employ the features of theinvention in connection with dry-hardening operations, but in disclosingthe invention it will be described in connection with a so-called wetprocess wherein objects to be treated are immersed in a fused salt bathwhich is heated to bring about the hardening efiect.

In the drawing, there is represented at 2 and 4 hardening furnaces whichmay consist of hardening pots or tanks, 6 and 8, suitably associatedwith combustion compartments. At G is represented a tank or tankscontaining a gas, such as ammonia, having nitrogen as an importantelement. The nitrogen-containing gas is caused to flow from the tanks Gto the furnaces, 2 and 4.

Ordinarily when ammonia gas is delivered directly to the furnace, it isnecessary to deliver very large amounts in order that the desired amountof active nitrogen be passed into the fused salts. According to thisinvention, as will appear, certain amounts of ammonia gas will rovide agreater proportion by volume of active nitrogen than has heretofore beenpossible.

The bath employed in the pots, 6 and 8, will preferably consist of fusedsalts containing more or less nitrogensuchas a bath including cyanidesalts which, as'is well known, contain nitrogen.

With such salts it is desirable to operate within a temperature rangefrom 950 to 1700 degrees F., while a temperature of 1400 degrees F., hasbeen I found to be especially satisfactory.

It will be appreciated that the nitrogen constituent of the bath isdissipated in the treating operation and it is to replenish thedissipated nitrogen supply that the invention in its broad aspect isdirected. As the ammonia gas leaves the tank, it is subjectedto'dissociating and ionizing or activating reactions. Preferably this isdone by electrolytic activating and dissociation so as to dissociate anddisunite the hydrogen and'nitrogen constituents of the ammonia. The gasmay flow from the tanks, G, to a dissociator unit and then through anactivator unit and thence to the furnace or furnaces. If preferred, theactivator unit may be nearest the furnace. This will depend onconditions.

As shown in Fig. 1, a dissociating unit, A, is connected to the tanks,G, by pipes 10 and 12, with suitable valves, 14, to facilitate the flowof gas from the tanks. An activator or ionizing unit, I, is connected tothe dissociator by means of a pipe, 16. A pipe, 18, connects the ionizerto a conduit, 20, and by pipes, 22 and 24, the conduit is connected tothe furnaces with valves 26 associated with said pipes.

As will be seen, the gas flows from the tanks through the dissociator,into the ionizer or activator and thence to a furnace or furnaces.Gauges, 28 and 30, for indicating pressure and a gauge, 32, forindicating the flow of the gas are provided.

When desired, the dissociator may be connected as shown by the dashlinesinstead of as shown by full lines. The ionizer or activator unit willnow be described. There are provided a hollow outer metallic shell, 36,and an inner hollow electrode member, 38, which are suitably associatedby an insulating base and cap, 40 and 42, respectively.

The cylinder, 36, is connected to one side of a high voltage line by aconnector, 44, and the central electrode, 38, is connected to the otherside of said line as indicated by 46. The upper part, 37, of the centralelectrode is preferably starshaped, as shown in Fig. 4, to provide amultiplicity of points, 41. When these parts, 36 and 38, are subjectedto high voltage there is, of course, a tendency for a sparking actiontherebetween but according to my invention the amperage used ispreferably such as to avoid sparking. The inlet pipe, 16, connects thecentral member either to the tank or the dissociator while the pipe, 18,connects the cylinder to adjacent apparatus such as the conduit, 20, orthe dissociator.

Ammonia gas from a tank or the dissociator passes upwardly within thecentral electrode, 38, and outwardly through tangential openings, 39,therein and then upwardly between the star member, 37, and shell, 36.The amperage is preferably about .2 at 10,000 or 12,000 volts so thatthere is produced a glow, or corona effect around the star, asdistinguished from an are. As the ammonia gas passes upwardly betweenthe star and shell, it is acted upon by the electrical action or ischarged to bring about an activating and ionizing eifect of the gas,thus electrolytically dissociating or disuniting the hydrogen andnitrogen constituents of the gas and maintaining the dissociationthereof.

The dissociated hydrogen and nitrogen may then pass directly from theionizing unit into the bath and, since the nitrogen constituent issubstantially active nitrogen, there is delivered to the bath from-agiven volume of ammonia gas a much larger amount of nitrogen by volumethan could be delivered thereto without the ionizing reaction.

It has been discovered that by the ionizing reaction it is possible toprovide approximately four volumes of active nitrogen from one volume ofthe original gas. Not only, therefore, does the ionizing make itpossible to deliver larger amounts of nitrogen but the nitrogen is freefrom the restraining effects of other elements so that it may performits desired functions in the bath with the utmost efllciency.

The dissociating unit A will now be described with reference to Fig. 2.A plurality of tubes 50, 52 and 54 are arranged concentrically. Thelower ends of the tubes are suitably fixed to a lower header 65. Theupper ends of tubes, 54 and 52, are associated with an upper flange, 56,and plate 58 while the tube 50 terminates below the member 58. The wholemay be enclosed in a suitable case.

A suitable catalyst to be described is carried between the cylinders ortubes as shown and suitable insulating material surrounds the outercylinder or tube. Openings, 62, are provided in the lower end of tube 52and a tube 64 extends between tubes 50 and 52 for receiving athermocouple unit.

Ammonia gas passes through pipe 10 into the unit, flows downwardlybetween tubes 52 and 54 upwardly between tubes 52 and 50 and downwardlythrough tube 50 and out the pipe 16. It

will be noted that the gas passes through the catalyst.

A tube 66 depends from the member 58 and is preferably hollow and madefrom silica or some equally suitable material. This has associatedtherewith one or more windings 68 which when connected to a source ofelectrical energy will bring about a heating of the gas.

As the gas passes through the unit the heating thereof together with theaction of the catalyst will dissociate or disunite the hydrogen andnitrogen of the ammonia gas so that the nitrogen element is active forits effects in the bath. The catalyst employed is preferably prepared inthis way.

The oxides of iron, aluminum and potassium are strongly reduced by theaction of a stream of hydrogen and then ground in benzine and mixed withparafllne. The resultant mixture is then spread over pieces of pumiceplaced in the dissociator. By this procedure, the catalyst as a whole isporous so as to permit the gas to flow therethrough and effect the mosteflicient reaction.

As previously stated, it is desired that the parts 36 and 38 of theactivator be included in a circuit of relatively high potential with theamperage maintained at about .2. This may be accomplished in the mannershown in Fig. 3.

The circuit including connections 44 and 46 may be coupled by means of atransformer 70 to a supply circuit '72 so that a higher voltage isestablished in the secondary circuit which includes the activator thanprevails in the supply or primary circuit '12.

The electrical apparatus including the ionizer may be carried within acasing for convenience in manipulation and operation and may takevarious forms to operate for the purpose intended.

A resistance or rheostat 74 is in series with a side of circuit 72 tocontrol current and a switch 76 provides a means for cutting the currentin and out. A light or signal 78 is, by means of connections 80 and 82,arranged to indicate when the switch '76 is closed and the rheostat isin operation. This indicates that the ionizer is in operation.

As has been stated, it is desirable to operate the ionizer withoutsparking. This is accomplished by adjusting the rheostat '14. Shouldsparking occur, however, a relay 86 closes a switch 8'! connected by 88and 90 to circuit '12. This circuit includes a signal or light 91 andwhen energized the operator is warned so that he may make the necessaryrheostat adjustments to overcome sparking.

A switch 93 is provided in association with 88 and 90 which may becalled a test switch. When closed with the arm of the relay in properposition the light or signal 91 is operated to indicate the relay isoperating properly.

It will be observed that as the ammonia gas passes through thedissociator unit that the hydrogen and nitrogen of the gas aredissociated or disunited so that the nitrogen is in a substantially freeactive form. This, as stated, is accomplished by subjecting the gas toheat and passing it through the catalyst whereby the nitrogen is in afree and substantially pure state for its reaction with the salts of thebath. The ionizer or activator furthers the dissociation reaction andfunctions to activate the nitrogen.

Having described the invention in the form at present preferred what Inow desire to claim and secure by Letters Patent of the United Statesis:

1. The method of treating steel objects which consists in, immersing theobjects in a fused salt bath including cyanide salts, subjecting a flowof ammonia gas to the action of an ionizing electrical discharge todisunite the gas into the hydrogen and nitrogen constituents thereof andimmediately passing the same into said bath whereby the nitrogenconstituent enters the bath as substantially free nitrogen.

2. The method of treating steel objects which consists in, immersing theobjects in a fused salt bath including cyanide salts, subjecting a flowof ammonia gas to the action of an ionizing electrical discharge todisunite the gas into its constituents, hydrogen and nitrogen,immediately passing the same into said bath whereby the said nitrogenconstituent enters the bath as substantially free nitrogen, andmaintaining said bath within a temperature range of from 950 to 1700degrees F.

3. The method of treating steel objects which consists in, immersing theobjects in a fused salt bath including cyanide salts, subjecting a flowof ammonia gas to electrolytic ionization to disunite the hydrogen andconstituents thereof, immediately passing the same into said bathwhereby the said nitrogen constituent enters the bath as substantiallyfree nitrogen, and maintaining said bath at a temperature ofapproximately 1400 degrees F.

4. The method of treating steel objects which consists in, immersing theobjects in a fused bath of nitrogen-containing salts, subjecting a flowof ammonia gas to electrolytic ionization to disunite the hydrogen andnitrogen constituents thereof and immediately passing the same into saidbath whereby the nitrogen constituent enters the bath as substantiallyfree nitrogen.

5. Thev method of treating steel objects which consists in, immersingthe objects in a fused bath of nitrogen-containing salts, subjecting aflow of ammonia gas to electrolytic ionization to disunite the hydrogenand nitrogen constituents thereof, immediately passing the same intosaid bath whereby the nitrogen constituent enters the bath assubstantially free nitrogen, and maintaining said bath within atemperature range of from 950 to 1700 degrees F.

6. The method of treating steel objects which consists in, immersing theobjects in a fused bath of nitrogen containing salts, subjecting a flowof ammonia gas to the action of electrolytic ionization to disunite thehydrogen and nitrogen constituents thereof, passing the same into saidbath whereby the nitrogen constituent enters the bath as substantiallyfree nitrogen, and maintaining said bath at a temperature ofapproximately 1400 degrees F.

VINCENT T. MALCOLM.

